Clogged filter indicator



M. F. KAUTZ ETAL 3,027,865

CLOGGED FILTER INDICATOR April 3, 1962 Filed Jan. 6, 1959 F INVENTOR.

3 MURRELL F. KAUTZ ELWYN H. OLSON ATTORNEY 3,027,865 Patented Apr. 3, 1962 3,027,865 CLGGGED FILTER INDICATOR lllurrell F. Kautz, Minneapolis, and Elwyn H. Olson, St. Paul, Minn, assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed Jan. 6, 1959, Ser. No. 785,212 6 Claims. (Cl. 116-114) The present invention is concerned with an improvement in a filter condition responsive device; in particular, in a device having a diaphragm for sensing the pressure across a filter in a forced air conditioning system, the diaphragm has a rigid center portion with a latch member attached slightly below the center of the diaphragm which is first to operate upon a slight change in the pressure across the diaphragm.

The present invention is concerned with an improvement in such pressure responsive devices which increases the accuracy of the device and yet provides for simplicity and therefore low cost of manufacture.

An object of the present invention is to provide an im- 2 proved filter condition responsive device.

Another object of the present invention is to provide a filter condition responsive device having a diaphragm with a center portion carrying a signal latching device which pivots about one edge upon a change in the pressure to insure that the opposite edge is first to move upon a slight change in pressure to operate the latching device.

These and other objects of the present invention will become apparent upon the study of the following specification and drawing of which:

FIGURE 1 is a front view of the filter condition responsive device.

FIGURE 2 is a side cross sectional view of the device as shown in FIGURE 1.

FIGURE 3 is a front view of the base of the condition responsive device of FIGURE 1 with the cover removed.

FIGURE 4 is an enlarged cross sectional fragmentary view of the pressure responsive diaphragm of the conditioning device as shown in FIGURE 2.

Refeiring to FIGURE 1, one embodiment of a filter condition responsive device is shown indicating visually the presence of a dirty or clogged filter. A chamber defining base 11) has a hollow cover 11. A window 12 in the cover is transparent; so that, when a flag or indicating device 13 is in a lower position, the presence of a dirty filter is visually indicated. When a reset knob 14 projecting from the front cover is turned in a clockwise direction, the flag is moved upward to reset the device. A set screw 15 is used to adjust the spring tension on the device for calibration purposes. When the device of FIGURE 1 is mounted on a panel and connected to a forced air conditioning system to respond to the pressure drop across a filter in the conditioning system, flag 13 will drop if the pressure reaches a predetermined value as determined by the position of set screw 15. After the flag 13 is seen in the lower position, the homeowner would change the filter and reset the condition responsive device by turning knob 14 clockwise to lift flag 13 upward in a relatched position.

Referring to FIGURE 2, a cross sectional side view of the device of FIGURE 1 is shown. A latch or ledge 20, which is attached to a flexible diaphragm 16 (shown in FIGURES 3 and 4) contained in the base 10, is held to the right by a force applied to the diaphragm by a spring 21 which is connected between an adjustable member 22 and a projecting ear 23 also attached to the diaphragm. When knob 14 is turned clockwise, an offset crank 24 attached to the knob engages flag 13 near its pivoted connection 25 to lift the flag to rest on latch member 20 in the position shown by the dotted lines.

When base 10 is mounted on a panel, conduit is connected to the space on one side of the filter in a conditioning system such as a forced air heating system. The pressure in the chamber is then reflected to the underside of the diaphragm. One manner of connecting the invention is to connect conduit 30 downstream the filter in a forcedair heating system when the fan is used to suck air through the filter and force the air into the space being heated. As the filter becomes dirty, the air is restricted in its movement through the filter and a partial vacuum is established downstream the filter. This partial vacuum is applied to the chamber or cavity on underside of the diaphragm to move the diaphragm to the left and unlatch flag 13.

In addition to 'a visual indication, an electric signal is available when flag 13 drops. 'A pair of metal contact springs 31 and 32 as shown in FIGURE 3 extend from the base. When the metal flag 13 drops in the position as shown in FIGURE 2, the flag acts as a shorting bar to'electrically connect the springs 31 and 32. When the springs are connected in a conventional signal circuit having a power source and an indicating operator or light by means of terminals 33 and 34, an electric signal is available upon the presence of a dirty filter.

Referring to FIGURE 3, diaphragm 16 is shown stretched across an opening or chamber 17 in base 10.

' into base 10. The clamping washer has a pair of projections or stops 41 and 42 extending downward from the upper edge to protrude out over diaphragm 16.

A pair of washers 47 and 43, as shown in FIGURE 4,

diaphragm to form a nonflexible or rigid center portion for the diaphragm. The washers are connected by means of rivet 44 through the center of the diaphragm. A member 45 which contains latch 20 and a pair of projecting portions 50 and 51 is also attached to the diaphragm by means of rivet 44. The latch member is located below the center of the diaphragm, and projecting portions 50 and 51 are above the center portion of the diaphragm so as to contact projections 41 and 42 respectively when the diaphragm is moved away from the base or outward as shown in FIGURE 3. Projecting ear 23 is connected to member 45; so that, the tension available from spring 21 pulls member 45 outward as shown in FIGURE 3; so that, projections 50 and 51 engage the underside of projections or fingers 41 and 42, respectively tending to pivot the rigid portion of the diaphragm formed by washers 47 and 43 in a clockwise direction as shown in FIGURE 4.

The tension on spring 21 is adjusted by the position of member 22 as shown in FIGURE 2. Member 22 can be moved horizontally back and forth along the guide rail or slot 55 by screw 15. Spring 60 maintains screw 15 to the left; so that, the head of the screw is held against cover 11.

Referring to FIGURE 4, a partial vacuum or an increasing negative pressure developed in conduit 30 and thus in chamber 17 on the left side of diaphragm 16 would tend to move the diaphragm to the left. Since the spring 21 provides a tension on the rigid portion of diaphragm 16 to hold projections 50 and 51. against the stops, the lower portion of washers 47 and 43 will be the first to move. The first movement causes latch 20 to move to the left to release flag '13. Without the pivotal connection between members 50 and 51 and projections 41 and 42, and the spring bias produced by spring 21 above the center of the diaphragm, a drop in the pressure in conduit 30 would not insure movement of latch 20 with any accurate regularity. For example without the stops connection, the upper portion of the diaphragm might be first to move. Such would require a greater change in the pressure in conduit 30 before the lower portion of the diaphragm moved to release flag 13. When pressure changes such as developed across a dirty filter in a forced air conditioning system are being sensed, a small irregularity in the sensing device is notdesired. If too great a pressure difference across the filter is required to operate the responsive device, the filter may be too dirty and cut down the efiiciency of the conditioning system. The present design provides a very accurate responsive device.

Under certain applications both sides of the diaphragm may be connected to the spaces on each side of the filter. A second conduit or opening 70 provides a connection between the space under air tight cover 11 or on the right side of the diaphragm as shown in FIGURE 2 and the conditioning system. Normally this conduit would be closed off, but when desired, the conduit can be opened by removing a thin section.

The invention has been described in one embodiment; however, the invention is intended only to be limited by the scope of the appended claims in which we claim:

1. A clogged filter indicator comprising a conduit, adapted for connection at one end to a duct between a. filter and a source of negative pressure, said conduit having a chamber-defining base on its opposite end, a flexible diaphragm connected to said chamber-defining base and forming with said base a chamber, a cover having a window therein over said diaphragm, said diaphragm having a member with a ledge on the side thereof opposite said chamber and an indicatingdevice pivoted on said cover and having contact with said ledge, whereby when said diaphragm is urged toward said conduit due to increased negative pressure therein, said indicating device will drop from said ledge and be visible to our observer, through said window.

2. The combination according to claim 1 wherein said cover forms a second chamber and a second conduit in said base connects to said second chamber so that a pressure differential across said filter is applied to said diaphragm through said first mentioned conduit and said second conduit.

3. The combination according to claim 1 wherein said member on said diaphragm has an upper portion which engages a portion of said base, and a spring connected between said cover and said member above a center of said diaphragm to bias said diaphragm and said member toward said cover so that upon an increase in said negative pressure said member pivots about said upper portion to move said ledge away from said indicator.

4. The combination according to claim 3 wherein said upper portion has two spaced projecting members which engage two spaced projecting members on said base'to provide a two point pivot for said member when said member is moved away from said cover by an increase in negative pressure.

5. The combination according to claim 1 wherein said member is biased toward said cover by a spring connected between a projection on said member above a center of said diaphragm and an adjustable connection on said cover so that the negative pressure needed to move said member toward said base can be selected by the tension on said spring.

6. The combination according to claim 1 wherein said indicating device comprises a conducting member and a pair of electrical terminals connected to said base so that upon said indicating device dropping to engage said terminals a close electrical circuit for signal purposes is provided.

References Cited in the file of this patent UNITED STATES PATENTS 

